1. Field of Invention
The present invention relates to an image processing method, and more particularly to a method for removing color fringe in a digital image.
2. Related Art
Color fringe is caused by incorrect setting of color at some positions of an image in an image system.
In a camera, color fringe is mainly resulted from lens aberration, sensor blooming, and color filter array interpolation (CFAI).
As glass has different refraction levels for light having different wavelengths, color fringe occurs to an image formed by a lens (a non-planar mirror). Thereby, the edges of an object are blurred due to a failure in precise calibration of different colors caused by lens aberration.
A sensor is a core member of a digital camera. In the digital camera, the sensor is used for capturing light rays passing through the lens and converting the light rays into electric signals. When the light rays are converged on the sensor through the lens, photodiodes of the sensor sense different quantities of charges under different light intensities and temporarily store the quantities of charges in a memory. After the quantities of charges are temporarily stored in the memory, a charge transfer circuit and a charge information read circuit then read the charge information in a clock pulse sequence and send the charge information to an analog-to-digital converter (A/D converter), so as to convert the charge information into a binary digit (that is, an electric signal) proportional to the light intensity. Moreover, the binary digit is data corresponding to a pixel. However, each photodiode can merely accumulate a certain quantity of charges within an exposure period. In a high luminance area, on one pixel, when the quantity of generated charges is too large and becomes saturated, the excessive charges may overflow to adjacent pixels and cause errors in data of the adjacent pixels. This phenomenon is referred to as blooming.
When color fringe occurs to a pixel and CFAI is performed, an incorrect pixel value is generated according to the wrong color, thus causing color fringe in the adjacent pixels.
In the prior art, a red, green, and blue (R/G/B) signal is generally used for detection, so as to find pixels with color fringe. However, as color fringe usually occurs in a bright area, the method may result in a failure of discovering a part of pixels with color fringe, let alone correcting these pixels.
Moreover, in the prior art, the correction method is a chrominance (Cb and Cr) suppression method or a method of suppressing red (R) signals and blue (B) signals to green (G) signals. Both methods may result in grayish images after correction.
Related technologies can be referred to in US Patent Application Publication No. 2007/0153341 and 2007/0097267.